1. Field of the Invention
The present invention relates to a recording layer of a magneto-optical storage medium having a sublayer, and more specifically, to a recording layer of a magneto-optical storage medium having a sublayer which is formed to be adjacent to the recording layer in order to increase a density of recording of the magneto-optical storage medium, thereby increasing a coercive force of the recording layer to enhance a magnetic stability of the magnetic domain, so that the size of the magnetic domain can be stably reduced, and a method for fabricating the recording layer.
2. Description of the Prior Art
In recent years, demands for a medium capable of recording and reproducing information with a high density have been increased. Accordingly, much attention has been also paid to a high density recording device using a laser beam. In particular, a magneto-optical storage medium can be used as a device capable of repeatedly recording and erasing information with a high density. Therefore, it is expected that researches and developments of the magneto-optical storage medium will proceed continuously and greatly.
In the magneto-optical storage medium, information is recorded by forming a magnetic domain in a vertically magnetized thin film with a laser beam and a magnetic field, and the information is reproduced by using a magneto-optical effect. The recording layer used in the magneto-optical medium is made up of an RE-TM alloy containing a rare earth element and a transition metal. The transition metal includes ferromagnetic elements such as Fe, Co, etc., and the rare earth element includes Tb, Dy, Gd, Sm, Ho, etc.
The most important purpose of the magneto-optical storage medium is to record information as much as possible in one unit area, that is, to increase the density of recording. Thus, in order to increase the density of recording, it is necessary that the size of the magnetic domain in the recording layer is reduced. In addition, it is necessary that the laser beam has a short wavelength since the recording and reproducing of the information is affected by the wavelength of the laser beam.
In the prior art, a red laser beam has been used as a light source for the recording and reproducing in the magneto-optical storage medium. According to the technologies having been developed up to now, the red laser bean used as the light source causes no problem to the magnetic stability of the magnetic domain, even if the size of the magnetic domain in the recording layer is adjusted to a suitable size. However, in the recently-developed technologies, the other laser beams having shorter wavelengths such as a green, a blue, and a ultraviolet laser beams have caused the following problems as the size of the magnetic domain in the recording layer is further reduced to increase the density of recording of the magneto-optical storage medium.
When the size of the magnetic domain in the recording layer is reduced below a predetermined threshold size, a physical effect, the so-called ‘super-paramagnetic effect’ occurs, so that the magnetization characteristics of the storage medium may be lost. Therefore, it is necessary that the magnetic stability of the recording layer should be ensured in order to reduce the size of the magnetic domain.
On the other hand, in the conventional magneto-optical storage medium, development has been focused on the technology for improving reproduction characteristics of the reproducing layer rather than that for ensuring magnetic stability of the recording layer. FIGS. 1 and 2 are cross-sectional views illustrating conventional magneto-optical storage media.
Referring to FIG. 1, a first dielectric layer 110, a reproducing layer 120, a second dielectric layer 130, a recording layer 140, and a third dielectric layer 150 are sequentially stacked on a substrate 100. As shown in an enlarged view in the right side of the figure, the reproducing layer 120 consists of multiple layers including magnetic layers and non-magnetic layers. The magnetic layers are made up of one of Co, Fe, Ni, and an alloy containing thereof. The non-magnetic layers are made up of one of Pt, Pd, Ag, Au, and an alloy containing thereof. The purpose of this structure is to increase a resolution of a signal of the recording layer being transferred to the reproducing layer.
FIG. 2 shows a method of increasing the resolution of the signal of the recording layer 270 by magnificently transferring the coercive force, which is transferred from the recording layer 270 to the first reproducing layer 240, to the second reproducing layer 220.
Most of the conventional technologies have been oriented to a way of solving the following problem. When the size of the magnetic domain is reduced to increase the density of recording, noises are disadvantageously introduced into the adjacent magnetic domains in the process of reproducing the magnetic domain having a smaller size than the diameter of the reproducing beam which has a shape of a spot. As a result, there is a problem that the signal to noise ratio is relatively lowered to cause a reproduction error. However, the conventional technologies can not overcome the super-paramagnetic effect that occurs additionally when the size of the magnetic domain is reduced.
Therefore, in order to increase the density of recording, it is required to overcome the super-paramagnetic effect which occurs when the size of the magnetic domain is reduced below a threshold size by ensuring the stability of the magnetic domain in the recording layer rather than by improving the reproduction characteristics of the signal.